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2003 gmc envoy_sle
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Discussion Starter #1
I've recently developed a 1.72 - 1.78 amp parasitic battery drain on my '03 GMC envoy. I've traced the draw to the HVAC-B fuse located in the under-seat fuse box. By pulling the HVAC-B fuse I can see on my multi-meter a gradual drop from somewhere in the 1.7 amp range to under 100 milliamps. With the fuse pulled the entire HVAC system is dead - not surprising. And with the fuse in the entire HVAC system functions just fine. I have no idea how many control modules are fed off this circuit but I'm assuming one or more of the control modules are not falling into sleep mode after the ignition is switched off. How do I isolate the parasitic drain any further? What modules might be suspect?
 

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2003 gmc envoy_sle
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3 Posts
Discussion Starter #3
The HVAC B fuse only feeds the HVAC control unit. That would be the likely suspect.

So I'm not sure I know what the HVAC control unit looks like. Is it the actual face unit with buttons and knobs that I see in the center of the console or is it some thing that lives under or behind the dash? Is there any way you can post a picture? Thanks!!!:thx
 

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2003 gmc envoy_sle
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Discussion Starter #4
Problem found!!! It turns out that I have a faulty rear climate control module. This is the HVAC module mounted into the center console that faces the rear seats and allows the backseat passengers to control their climate. After looking up a wiring diagram for the HVAC system I could see that power to the rear climate control module is via the center console HVAC Climate Control Module (which in turn is fed from the HVAC-B circuit/fuse.

It was recommended on another board that I disconnect the rear climate control module - which after some experimenting turned out to be pretty easy since the control module simply pops out of the rear console with a little help from a small flat screw driver. Once the module was outside the console I could easily disconnect the wiring harness feeding it.

With the wiring harness disconnected I tested the draw with my multimeter and after a couple of minutes the draw dropped below 0.00 amps. Just to be sure I plugged the module back in and the amp draw went up to 1.75 - 1.80 and held constant, indefinitely. After 30 minutes I disconnected the rear HVAC module again and after a couple of minutes the draw, as expected, dropped below 0.00 amps.

I just looked out at e-Bay and can find a used, warrantied rear HVAC control module for $39 plus shipping. Considering that I've only used the rear temperature control module about 3 times since I bought my '03 Envoy new it's no big deal if I ever replace it.

Now I can leave the HVAC-B fuse in while the ignition switch is off and not worry about waking up to a dead battery. Thanks everyone for all your help!! :thx
 
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